NASA | GSFC | STScI | HubbleSite | 2019 Jul 02
Two NASA space telescopes have teamed up to identify, for the first time, the detailed chemical "fingerprint" of a planet between the sizes of Earth and Neptune. No planets like this can be found in our own solar system, but they are common around other stars.This artist's illustration shows the theoretical internal structure of the
exoplanet GJ 3470 b. It is unlike any planet found in the Solar System.
Weighing in at 12.6 Earth masses the planet is more massive than
Earth but less massive than Neptune. Many planets of this mass exist
in our galaxy. Credits: NASA, ESA, and L. Hustak (STScI)
The planet, Gliese 3470 b (also known as GJ 3470 b), may be a cross between Earth and Neptune, with a large rocky core buried under a deep crushing hydrogen and helium atmosphere. Weighing in at 12.6 Earth masses, the planet is more massive than Earth, but less massive than Neptune (which is more than 17 Earth masses).
Many similar worlds have been discovered by NASA's Kepler space telescope, whose mission ended in 2018. In fact, 80% of the planets in our galaxy may fall into this mass range. However, astronomers have never been able to understand the chemical nature of such a planet until now, researchers say.
By inventorying the contents of GJ 3470 b's atmosphere, astronomers are able to uncover clues about the planet's nature and origin. ...
Astronomers enlisted the combined multi-wavelength capabilities NASA's Hubble and Spitzer space telescopes to do a first-of-a-kind study of GJ 3470 b's atmosphere.
This was accomplished by measuring the absorption of starlight as the planet passed in front of its star (transit) and the loss of reflected light from the planet as it passed behind the star (eclipse). All totaled, the space telescopes observed 12 transits and 20 eclipses. The science of analyzing chemical fingerprints based on light is called "spectroscopy." ...
Fortuitously, the atmosphere of GJ 3470 b turned out to be mostly clear, with only thin hazes, enabling the scientists to probe deep into the atmosphere.
"We expected an atmosphere strongly enriched in heavier elements like oxygen and carbon which are forming abundant water vapor and methane gas, similar to what we see on Neptune", said Benneke. "Instead, we found an atmosphere that is so poor in heavy elements that its composition resembles the hydrogen/helium rich composition of the Sun." ...
Probing a New Class of Exoplanets
California Institute of Technology | 2019 Jul 02
Probing a New Class of Exoplanets
University of Montreal | 2019 Jul 02
A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted
Atmosphere and Mie-Scattering Clouds ~ Björn Benneke et al
- Nature Astronomy (online 01 July 2019) DOI: 10.1038/s41550-019-0800-5
- arXiv.org > astro-ph > arXiv:1907.00449 > 30 Jun 2019